Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

[Fortran90] how to write increment in dimension

  1. Aug 6, 2013 #1
    hi all,

    i am new with fortran 90. i have here codes for 2d fdtd polar coordinates. but i have problem handling with increment in dimension in real number (as higlighted below). I have googled how to write the increment in do loops, but do loops only applicable for integer. can anyone help me how to solve this.

    thank you

    Code (Text):

    !2d polar coordinates
    !reference: Numerical electromagnetic: fdtd method (Umran S Inan, R Marshall)

    subroutine test3
    implicit none

    double precision                   :: f0,miu0,eps0
    double precision                   :: delta, dt,dr,dp
    double precision                   :: vp,lam0,rph,rmh           !lam0 = lambda          
    integer                                 :: pp
    integer                                 :: rr,m,n
    integer                                 :: t
    integer                                 :: i,j
    double precision,dimension(202,202) :: x,y
    double precision,dimension(202,202) :: Ez,Hp,Hr    !Ez,Hy,Hx
    double precision                   :: Ein
    double precision, parameter  :: pi = 3.14159265
    double precision                   :: r
    double precision                   :: p  
    character(len=20)                 :: filename

     f0   = 30.e9
     miu0 = 4.0*pi*1.0e-7
     eps0 = 8.854e-12
     vp   = 1/sqrt(eps0*miu0)
     lam0 = vp/f0
     dr   = 0.05*lam0
     dt   = dr/vp
    ! space grid 201x201      
     rr = 201
    [COLOR="Blue"] r = ,dr*(rr-1),dr[/COLOR]

    !define deltaphi so that there are 200 points in 2pi rad
     dp = 2*pi/200        !in rad

    [COLOR="Blue"] p = 1,2*pi-dp,dp[/COLOR]
    pp = size(p)

    !initialize Ez,Hp,Hr to zero at t=0
    do m = rr,pp
     do n = rr,pp
      Hp(m,n) = 0
      Hr(m,n) = 0
      Ez(m,n) = 0
     end do
    end do

    ! coodinate transformation
    do m = rr,pp
     do n = rr,pp
      x(m,n) = 0.0
      y(m,n) = 0.0
     end do
    end do

    do m = 1,rr
     do n = 1,pp
      x(m,n) = r(m)*cos(p(n))
      y(m,n) = r(m)*sin(p(n))
     end do
    end do

    do t = 1,200
      write (filename, "('data',I3.3,'.dat')") n
      open (unit=130,file=filename)
    !initiate sinusoidal wavepulse at center
    !  Ein  = 0.0
    !  Ein(t) = sin(2*pi*f0*t*dt)
      Ez(1,1) = sin(2*pi*f0*t*dt)
      !print *, 'Ein(t)=',Ein(t)

    !update magnetic field equation for Hr
      do m = 2,rr
       do n = 1,pp-1
        Hr(m,n) = Hr(m,n) - ((dt/miu0/r(m)/dp)*(Ez(m,n+1) - Ez(m,n)))
        !print *,'i=',i,'j=',j,'Hr(i,j)=',Hr(i,j)
       end do
      end do

    ! correction for 2pi continuity
      do m = 2,rr
       Hr(m,pp) = Hr(m,pp) - ((dt/miu0/r(m)/dp)*(Ez(m,1) - Ez(m,pp)))
      end do

    !update magnetic field for Hp
      do m = 1,rr-1
       do n = 1,pp
        Hp(m,n) = Hp(m,n) + ((dt/miu0/dr)*(Ez(m+1,n) - Ez(m,n)))
        !print *,'m=',m,'n=',n,'Hp(m,n)=',Hp(m,n)
       end do
      end do

    !fix end point where phi = 2pi
      do m = 2,rr
        Ez(m,1) = Ez(m,1)+(dt/eps0/r(m)/dr)*(rph*Hp(m,1)-rmh*Hp(m-1,1))&
      end do

    !update electric field equation
      do m = 2,rr
       do n = 2,pp
        rph = r(m)+dr/2
        rmh = r(m)-dr/2  
        Ez(m,n) = Ez(m,n)+(dt/eps0/r(m)/dr)*(rph*Hp(m,n)-rmh*Hp(m-1,n))&
    !    write (130,*) m,n,Ez(m,n)
    !    if (m == 200) write (130,*) ' '
       end do
      end do

    close (unit=130)

    end do !n

    end SUBROUTINE test3

  2. jcsd
  3. Aug 6, 2013 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Your assignment statements in blue for r = and p = don't make sense in Fortran.

    If you want to create a series of real values for r and p which are equally spaced,
    then define r and p as real arrays. You already know the size of the array you will need given the
    number of points you want to create in the interval. Arrays in F90 can be dimensioned in a flexible fashion
    depending on your requirements.

    See: http://www.cs.mtu.edu/~shene/COURSES/cs201/NOTES/F90-Array.pdf

    You can also use the implied do loop to initialize the values of your arrays.
  4. Sep 8, 2013 #3
    actually i have matlab code and trying to write in fortran. however i have problem with the interval part for r and p. however, for r i have write it id do loops
    Code (Text):

    !increment r = 1,dr*(rr-1),dr
    do ir = 1,rr-1
      r(ir) = (ir-1)*dr
      !print *, 'ir=',ir,'r=',r
    end do
    and it is work. but i have problem with p, which is for p the last value should be 2*pi-dp, with the intervalor increment is dp...and size for p is 200. ( p=0:2*pi-dp:dp). can anyone teach me how to write this increment using do loop.

    thank you
  5. Sep 9, 2013 #4
    Code (Text):

    n  = 200
    dp = 2*pi/n
    do ip = 0,n-1
       p = ip*dp
    end do
    By the way, your loop in the previous post seems short one extra dr...by having ir go from 1 to (rr-1) and additionally multiplying dr times (ir-1)...you have one extra -1; also, you may not want to go from 1, but 0 as my example shows to go from 0 to 2*pi-dp
  6. Sep 9, 2013 #5
    thank you gsal. it's work perfectly.
    Last edited: Sep 9, 2013
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook